Analysis of psychoacoustic responses to digital music for enhancing autonomous creative systems Omar López-Ortega ⇑ , Anilú Franco-Árcega Área Académica de Sistemas Computacionales, Universidad Autónoma del Estado de Hidalgo, Carretera Pachuca-Tulancingo, km. 4.5, C.U., C.P. 42084 Pachuca, Hidalgo, Mexico article info Article history: Received 28 November 2013 Received in revised form 11 August 2014 Accepted 26 September 2014 Keywords: Emotions Psychoacoustics Clustering Fractals Digital music abstract In the present article the authors describe a psycho-acoustics study aimed at obtaining data for the enhancement of creative systems. Specifically, it is provided an analysis of the emotional responses pro- voked by fractal-generated music, establishing the link between input parameters from which a given musical piece is generated, and the emotion provoked. This analysis constitutes the basis to elevate com- puter-assisted creativity: Our ultimate goal is to create musical pieces by retrieving the right set of parameters associated to a target emotion. This paper contains the description of (i) a method to evaluate the emotional responses to fractal-generated music fragments, (ii) acoustic settings and protocol, (iii) analysis of the emotional responses given by human listeners. Even though similar experiments whose intention is to elucidate emotional responses from music have been reported, this study stands because a connection is appointed between fractal-generated music and emotional responses, all with the pur- pose of advancing in computer-assisted creativity. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction The perception of complex sounds provokes effects on emotions and mood. This process contributes to the construction of concepts that make up our reality. Music, being a complex sound itself, is used to enact emotion regulation, communicative expression, identity construction, and interpersonal coordination [1]. Music influences strongly on emotions and our cognitive system [2], indi- cating the involvement of the central nervous system through inte- gration and interpretation together with peripheral auditory processing. However, it is not the physical sound parameters underlying music but the corresponding auditory qualities per- ceived by the auditory system that cause the effect on emotions. Hence the quantitative relations between the auditory stimuli and the perceived emotions are of particular importance for the realization of music [3]. Psychoacoustics is paramount to achieve this goal. Emotions are defined as episodes of synchronized body responses, indicating the valuation of an event and leading to a ser- ies of reactions of limited duration [4]. Despite being difficult to characterize, they have been framed in several forms. The Circum- plex Model of Affect (CMoA) developed by Rusell [5,6] classifies them according to two dimensions: Valence and Arousal. Valence refers to the degree of attractiveness or aversion that an individual feels towards, in this case, an emotion. Arousal measures to what extent an emotion leads to action or to physiological readiness for activity, thus defining a state in which bodily resources are mobilized, including the peripheral nervous system, the endocrine system, and the immune system [2]. Attempts to create music by computer systems abound. Some developments include the creation of musical pieces from the Mandelbrot set [7], non-linear models such as cellular automata [8,9], genetic algorithms [10,11], or swarm computing [12–14]. DNA-like data has been transformed into music [15]. Melodic sequences have been generated by using the Chua’s circuit [16]. Our own work on computer assisted creativity is reported in [17,18]. However, whether musical pieces created by computers can lead to an emotional response is still an open question. If it is true that emotional reactions can be enacted by digitally created music, then it is attainable to find the link between the input data (used to create musical pieces) and emotions. This article builds a bridge between acoustics and computer systems that assist in the creation of musical pieces. This bridge is built through obtaining, organizing, and analyzing data. Acous- tics is applied successfully to obtain the emotional responses per- ceived when fractal music acts as auditory stimulus. Then, we proceed to find the relations between the input parameters on http://dx.doi.org/10.1016/j.apacoust.2014.09.027 0003-682X/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail addresses: lopezo@uaeh.edu.mx (O. López-Ortega), afranco@uaeh.edu.mx (A. Franco-Árcega). Applied Acoustics 89 (2015) 320–332 Contents lists available at ScienceDirect Applied Acoustics journal homepage: www.elsevier.com/locate/apacoust